1. Field of the Invention
The present invention generally relates to the field of diagnostic techniques for nuclear reactor subsystems in a nuclear steam supply system. More particularly, the present invention is directed to a control element drive mechanism (CEDM) in such nuclear power plants.
2. Description of the Related Art
In a typical pressurized water nuclear power reactor, a plurality of control element assemblies with associated drive mechanisms (CEDMs) are supported on a nuclear reactor vessel for moving the control element assemblies into and out of the reactor core, for the purpose of controlling the gross power level, or the power distribution in the core. Typically, each control element assembly (CEA) has a shaft which is driven by a CEDM. Such CEDMs each include a plurality of electromagnetic coils having latches which engage grooves on the shaft of the CEA, whereby the shaft may be moved in step-wise fashion. The shaft terminates in a web or similar structure, which supports a plurality of individual control elements or rods sized to pass through openings within or between fuel assemblies which define a reactor core.
A particular nuclear reactor may have dozens of CEAs, which are typically grouped or ganged in sets or four or eight, so as to move in unison when actuated by respective control element drive mechanisms. In the event of an emergency, the CEAs can be disengaged from their respective drive mechanisms, thereby falling under force of gravity into the reactor core to shut down the reactor power as quickly as possible. This free fall of a CEA is also known as a rod-drop.
The position and movement of each CEA and, hence, its associated control rods, is typically sensed by a reed switch position transmitter which produces an analog position output signal that is sent to a safety control system during normal operation of the power plant. This signal can be used within the safety control system as part of a calculation to determine if the reactor should be tripped, thereby causing the rods to drop.
Nuclear steam supply system plants such as those described above routinely perform post-refueling rod testing prior to power ascension. The testing normally consists of a CEDM operational test, withdrawal and insertion of the rods, a rod coupling verification test, a rod-drop test from a small height, and a full height rod-drop, on each CEDM. Such testing is normally performed at reactor operating temperature and pressure. Data is acquired during the CEDM operational tests and analyzed to verify that the nuclear steam supply system is fully operational before normal power ascension occurs. This data can then be used for troubleshooting or to generate outage reports according to governmental regulations. Further due to governmental regulations, the data acquired during CEDM operational testing must be archived for possible review in the future.
In the related art, electromechanical data collection apparatus (typically analog strip chart recorders such as the Honeywell Visicorder) are utilized to record coil-current within the control element drive mechanisms and, optionally, the signal outputted from the reed switch position transmitters. Typically, the test data is collected in a "cable spreader" room in which the CEDM control cabinet is located. Since testing occurs on a periodic basis, test points for electrically connecting the data collecting apparatus are permanently provided in the control cabinet.
However, data recorded in such a manner results in signal traces being displayed on long continuous rolls of paper which is expensive, bulky in storage and extremely difficult to manipulate when manual trace analysis occurs. Furthermore, such electromechanical systems are prone to mechanical failure thereby further increasing testing delays and increasing expense.
Still another deficiency of the above-described electro-mechanical systems is that, due to the limited recording capability of such systems, CEDM operational testing must be performed on one CEA at a time. In particular, this is due to the fact that each drive mechanism typically employs four or five electromagnetic coils to position the associated CEA and one reed switch position transmitter is associated with each CEA. Thus, each CEDM operational test entails recording up to six parameters of data per CEDM tested. Because the known mechanical recording apparatus can only record six parameters at a time, all CEAs in a group (consisting of four or eight CEAs) cannot be tested simultaneously. Rather, multiple tests must be run (four or eight as the case may be) to verify performance of all of the drive mechanisms associated with the CEAs of the group.
The above-described deficiencies of the related data acquisition systems, thus, include increased testing expenses, prolonged testing operations, difficulty in analyzing and storing recorded data and a likelihood of mechanical failure of the test equipment.
Accordingly, there remains a need in the art for a CEDM data acquisition system which overcomes the aforementioned deficiencies by simplifying data gathering, storage, and manipulation for, e.g., troubleshooting, generation of outage reports, and data archiving.
There remains an additional need in the art for an improved CEDM data acquisition system which overcomes the aforementioned deficiencies by permitting simultaneous recordation of data pertaining to all of the CEDMs in a CEA group while not requiring any modification of the nuclear power plant.
There remains a further need in the art for a CEDM data acquisition system which overcomes the aforementioned deficiencies by providing continuous and interactive CEDM test monitoring on an easy to read and analyze color display, such monitoring occurring while the CEDM operational tests occur.
There remains yet another need in the art for a CEDM data acquisition system which overcomes the aforementioned deficiencies of the related art by providing a test data display which has the capability to automatically change the parameters displayed upon the occurrence of a predetermined triggering event such as a rod-drop event.